Windings having continuous shields therearound



United States Patent 3,393,388 WINDINGS HAVING CONTINUOUS SHIELDS THEREAROUND George V. Young, 4318 Coronet Drive,

Enciuo, Calif. 91316 Continuation of application Ser. No. 296,276, July 19, 1963. This application Mar. 14, 1967, Ser. No. 623,139

8 Claims. (Cl. 336-84) ABSTRACT OF THE DISCLOSURE This invention relates to a bobbin and coil assembly. The bobbin is made of plastic material having first and second conductor windings mounted thereon with the second conductor winding insulated from the first winding; Each conductor winding is wholly encased in a separate continuous unbroken envelope of electrically conducting material having a resistance of from .01 to 100 ohms per square inch per unit of thickness. The envelopes are in non-conducting relationship with each other and thus isolate one Winding from the other.

This application is a continuation of application Ser. No. 296,276, filed July 19, 1963, now abandoned.

This invention relates to electrostatically shielded transformer coil windings.

An object of the invention is to provide an improved bobbin and coil winding assembly for transformers which is less expensive than previous assemblies and yet has excellent electrostatic shielding characteristics.

Another object is generally to provide an improved electrostatic shield for inductor coil windings which are mounted adjacent each other on a common bobbin.

The above and other objects, features and advantages of the invention will be more fully understood from the following description of the invention considered in connection with the accompanying illustrative drawing in which:

FIG. 1 is a top plan view of a bobbin and coil winding assembly in accordance with the invention, showing the core of a transformer associated with the assembly in dot-dash lines;

FIG. 2 is a vertical sectional view taken on line 22 of FIG. 1;

FIG. 3 is a vertical sectional of FIG. 1; and

FIG. 4 is a detailed sectional of part of the assembly.

Referring now to the drawing in detail, the bobbin carries a primary electric winding 12 and a secondary electric winding 14 which is insulated from the primary winding. The bobbin is mounted on the intermediate leg 16 of a laminated core 18 of a transformer 20, the laminations of the core being held together by screws 22 which may be used to mount the transformer on a plastic support 24, as illustrated by FIG. 3.

Bobbin 10 is electrically non-conducting and comprises an elongated hollow sleeve, square in cross section, as provided by the square inner wall 26 which has an outer core winding supporting surface 28. The opposite ends of the wall are provided with square flanges 30 which extend outwardly from surface 28, transversely of the latter. An intermediate square flange 32 is positioned midway between end flanges 30 and also extends outwardly from surface 28 to divide the bobbin into two coil winding channel carrying sections.

The bobbin is made of an electrically non-conducting material which has good dimensional stability characteristics under operating conditions. Diallylphthalate plastic material has been discovered to possess excellent charview taken on line 3-3 view, on a larger scale,

acteristics for the bobbin and is readily moldable to form the bobbin in a relatively inexpensive manner. Other examples of bobbin material possessing the necessary characteristics are nylon and trifiuorochloroethylene, sold under the trademark Kel-F.

To provide the necessary electrostatic shielding between windings 12 and 14, surface 28 of the bobbin and the surfaces of the confronting sides 34 of end flanges 30 and sides 36 of intermediate flange 32 are painted with electrically conducting material 38. Silver paint has been discovered to possess the required shielding properties. The shield resistance of the conductive material should be from .01 to ohms per square inch per unit of thickness of the shield. If the shield has too high a specific resistance, then the shielding will be inadequate. On the other hand, if the resistance is too low, then the shield will act as a shorted turn and cause excessive heating of the transformer as well as other adverse effects. Silver paint'has about .1 ohm resistance per square inch per unit of thickness. Other materials which may be used are gold or copper paint.

The windings 12 and 14 are positioned in the respective channels of the bobbin and extend peripherally around the bobbin with the inner surface of each winding in contact with the conductive paint 38 coating surface 28 of the bobbin and with the opposite sides of the winding in contactwith the conductive paint on the surfaces of the confronting sides 34 and 36 of the respective channel. The outer surface of each winding is covered with a strip 40 of insulating material, for example, tape sold under the trademark Mylar, and the outer surface of the strip is coated with the conductive paint 38, as best seen in FIGS. 3 and 4, and this latter coating is in electrical conducting contact with the side coatings to encase the respective winding in an electrically conducting envelope which forms the electrostatic shield. The terminal wire ends of each winding extend through the envelope, in any suitable manner (not shown) for connection to their respective connecting leads.

While I have shown and described the preferred embodiment of the invention, it will be understood that the invention may be embodied otherwise than as herein specifically illustrated or described, and that certain changes in the form and arrangement of parts and in the specific manner of practicing the invention may be made without departing from the underlying ideas or principle of this invention within the scope of the appended claims.

I claim:

1. In combination, an insulating bobbin, a first conductive winding mounted on said bobbin, a second conductive winding mounted on said bobbin and insulated from said first winding, a continuous, unbroken envelope of electrically conducting material wholly encasing said first winding, and another continuous, unbroken envelope of electrically conducting material wholly encasing said second winding and in non-conducting relation with said first mentioned envelope, so that said windings are isolated one from the other by said envelopes of conducting material, the electrical resistance of said electrically conducting material being in the range of .01 to 100 ohms per square inch per unit of thickness.

2. The combination of claim 1, wherein said bobbin is made of plastic material comprising one of the class consisting of diallylphthalate, nylon and trifluorochloroethylene, and said electrically conducting material comprises one of the class consisting of finely divided particles of gold, silver and copper bound together by a bonding agent.

3. In combination, an insulating bobbin comprising a longitudinally extending sleeve member having a peripherally endless supporting surface, a pair of longitudinally spaced, W peripherally endless, wardly from said supporting surface, an intermediate, peripherally endless flange positioned between said end flanges and extending outwardly from said supporting surface and thereby dividing said bobbin into two channel sections, a first continuous, unbroken layer of electrically conducting material covering said supporting surface and the confronting sides of said intermediate and one of said end flanges in one of said channels, a second continuous, unbroken layer of electrically conducting material covering said supporting surface and the confronting sides of said intermediate and the other of said end flanges in the other of said channels, a first transformer winding in 'said one of said channels, a second transformer winding, insulated from said first winding, and positioned in said other channel, a continuous, unbroken layer of electrically conducting material disposed about the outer side of said first winding and in electrical conducting contact with said electrical conducting material covering said confronting sides of said intermediate flange and said one end flange and forming an envelope totally enclosing said first winding, and another continuous, unbroken layer of electrically conducting material in non-contacting relation with said last mentioned layer and disposed about the outer side of said second winding and in electrical conducting contact with said electrical conducting material covering said confronting sides of said intermediate flange and said other end flange and forming an envelope totally enclosing said second winding, the electrical resistance of said electrically conducting material being in the range of .01 to 100 ohms per square inch per unit of thickness, said conducting material wholly encasing said windings whereby to isolate one winding from the other with said conducting material.

4. The combination of claim 3, wherein said layers end flanges extending outcomprise one of the class consisting of finely divided particles of silver, gold and copper bound together by a bonding agent.

5. The combination of claim 3, and a layer of insulating material covering said outer surface of said first winding and extending peripherally around said first winding, and another layerof insulating material covering said outer surface of said second winding and extending peripherally around said second winding, said layer of electrically conducting material for. said outer side of said first winding being in contact with-the outer surface of said first mentioned layer of insulating material, and said covering layer of electrically conducting material forsaid outer surface of said second winding being in contact with the outer surface of said other layer of insulating material.

6. The combination of claim 5, wherein said electrically conducting material is a coating.

7. The combination of claim 6, wherein said bobbin is made of plastic material comprising one of theclass consisting of diallylphthalate, nylon and trifluorochloroethylene.

8. The combination of claim 6, wherein said coating. comprises one of the class consisting of finely divided particles of silver, gold and copper in a binding.

References Cited UNITED STATES PATENTS 2,420,311 5/ 1947 GoWel-l 174355 2,914,719 11/1959 Walton et al 336-84 X 3,131,371 4/1964 Brekke et al 336--2O8 X 3,173,115 3/1965 Peuron 336-70 X DARRELL L. CLAY, Primary Examiner. 

